Ford Repair: 1997 Ford Aerostar check engine light, 1997 ford aerostar, ford aerostar

Question
Check engine light is on. Had the code ran at local auto parts house. Code is po401. Also offered was ECM has detected too little flow on the EGR system with probable causes blocked passage on EGR system. Probable causes are blocked passage on EGR, failed EGR valve, EGR solenoid faulty, failed EGR pressure sensor where applicable and failed EGR position sensor where applicable. Where do I start?

Answer
This is one of what I call the Easter egg codes. You have two parts to look at, at the minimum. The first would be the DPFE sensor. The second is the EGR Valve. Also make sure the EGR Valve has proper vacuum. I hate to be so vague, but that is the nature of this code. Also, as if you needed anything else to look at, when removing the EGR Valve, clean the EGR (tube)for a possible carbon build up.